BIRMINGHAM, Ala. -- Heavyweight world titleholder Deontay Wilder did not show his usual zip, and he was not using his surgically repaired right hand much. Then he finally let a big bomb of a right go in the fifth round.

It's Wilder's best punch, and it was destructive.

That shot, along with a left hand behind it, crashed into Gerald Washington's head, causing Washington to slump into the ropes and fall to the mat. It was essentially the end of the fight as Wilder scored a fifth-round knockout to retain his world title for the fifth time Saturday night at Legacy Arena in the main event of a Premier Boxing Champions card on Fox in prime time.

"I knew he was going to come in excited to fight for a world title," Wilder said. "I just kept calm and found my rhythm. I knew he was going to tire out, and when he did I took advantage. It was all about timing. I'm very smart in the ring when it comes to using different tactics in the ring."

Deontay Wilder's knockout victory over Gerald Washington on Saturday could set up a world title unification bout later this year against New Zealand's Joseph Parker. David A. Smith/Getty Images

Wilder was facing big underdog Washington because the original opponent, Poland's Andrzej Wawrzyk -- who also would have been a prohibitive underdog -- was dropped from the fight. Wawrzyk came up positive for performance-enhancing steroids in random urine tests conducted by the Voluntary Anti-Doping Association in mid-January. Washington, 34, of Vallejo, California, stepped in as a replacement two weeks later.

Washington put up a solid fight, better than most would have expected. He gave Wilder (38-0, 37 KOs) some problems with his jab, but Wilder's tremendous power in his right hand is the great equalizer. At the time of the knockout, Wilder was ahead 39-37 on one scorecard, and the two other judges each had the fight 38-38.

"Washington fought well for the first couple of rounds," promoter Lou DiBella said. "I thought Washington frustrated Deontay a little bit, but then the power took over. He caught him, and it was goodnight."

Washington (18-1-1, 12 KOs), a former football player at Southern California who spent time on various NFL practice squads before coming to boxing, must have landed something decent early because Wilder's left eye looked a bit marked up by the third round. But both fighters were tentative for much of the fight.

Everything changed in the fifth round when Wilder, 31, from nearby Tuscaloosa, Alabama, landed the booming right hand.

"I just got a little impatient," Washington said. "I was trying to go for it. It was an even boxing match. I could have kept it like that and kept it boring. I don't know why I fell asleep there. I guess I lost a little focus.

"I caught him with one shot when he was coming in. But instead of me keeping that play going and keep pushing him back and keep him in control by keeping him in the center of the ring, I tried to get on him. I was trying to play a little counter punch role and catch him coming in. He just caught me."

Although Washington beat the count, he was unsteady, and Wilder attacked him with abandon. He rained shots, many of which landed flush and sent Washington's head snapping all over the place like a bobblehead doll. Washington was taking huge punishment when referee Mike Griffin tried to step in to call off the fight, but both fighters kept firing, and Griffin let it go.

But when Wilder caught Washington again and snapped his head back, Griffin jumped in and waved off the fight at 1 minute, 45 seconds.

Washington was still on his feet but was staggering and using the ropes for support as the raucous pro-Wilder crowd of 12,346 cheered and began singing loudly along with the public address system's playing of "Sweet Home Alabama."

"Fighting here in Alabama is a blessing," Wilder said. "The people here show up to support me and I love them for it. I'm always going to support and be here for my Alabama family. To see the crowd's response tonight meant a lot to me."

Wilder, who earned $900,000 to Washington's $250,000, landed 33 of 113 punches (29 percent), and Washington landed 30 of 98 (31 percent), according to CompuBox punch statistics. But Wilder landed nine power shots in the fifth round after landing just 11 in the previous four rounds, and Washington could not take the heat.

"It's just an experience. You have to follow the game plan and stay focused, stay patient," Washington said. "You may not get all the shots you want in the beginning, but you have to play the game all the way out and then things will start to happen."

The victory was a welcome relief for Wilder after a difficult period that began last May when he was supposed to make a mandatory defense against highly regarded Alexander Povetkin in Moscow. That fight was canceled nine days beforehand after Povetkin tested positive for the banned substance meldonium in a VADA test.

Wilder returned home and demolished faded contender Chris Arreola in an eighth-round knockout at Legacy Arena in July, but Wilder broke his right hand and tore his right biceps in the fight. He had surgery for both injuries and was out for the rest of 2016 before dealing with the opponent change for Saturday's fight. Wilder also had to miss eight days of training camp a few weeks ago to travel to cold and snowy New York in order to attend the civil trial for the lawsuit that he and DiBella brought against Povetkin and Russian promoter Andrey Ryabinsky for breach of contract over the cancellation of the fight.

Wilder won the case and then the fight against Washington, which could set up a world title unification bout later this year against New Zealand's Joseph Parker, who was ringside to scout Wilder.

"As I've been saying, I'm looking to unify the division," Wilder said. "I think it's critical to have one fighter and one champion, and that's Deontay Wilder. Let's hope Joseph Parker is ready for me because I'm definitely ready for him."

Parker (22-0, 18 KOs) first has to retain his title against his mandatory challenger, England's Hughie Fury (20-0, 10 KOs), on May 6 in Auckland, New Zealand, but Parker said during the week that he also wants Wilder later this year.

"That's the fight Deontay wants, and he's the boss," DiBella said. "We will sit down and talk about it, but we have to see what happens with Parker and Fury."

Wilder will be watching that fight with interest.

"I'm ready for Joseph Parker, but is he ready for me?" Wilder said. "I did my business. Now it's time for him to do his."